PROJECT SUMMARY The number one preventable cause of death in the world is tobacco use. Cigarette smoking in particular, costs an estimated $300 billion due to expenses related to medical care and lost productivity. Despite similar smoking prevalence rates, Blacks suffer disproportionately from smoking-related harms compared to Whites. Sleep disparities such as shortened sleep duration, shorter circadian periodicity, earlier chronotype, and increased variability of sleep timing have been reported more frequently in Blacks compared to Whites. Given that poor sleep quality predicts relapse from smoking cessation programs, particularly among socioeconomically disadvantaged adults, sleep deficiencies and irregular timing of sleep may impact smoking craving and withdrawal symptoms over the course of the 24-hour day. Surprisingly, few studies have examined these temporal patterns of smoking and craving, and none with regard to sleep disruption, chronotype or racial disparities. A better understanding of these factors may explain heterogeneity within the smoking population, especially in minorities. Thus, the purpose of this proposal is to test the central hypothesis that the impact of chronotype and impaired sleep on cigarette usage as well as smoking dependence, urge/craving, and withdrawal depends on race. Three specific aims will determine: contributions of sleep timing and sleep quality and quantity to racial disparities in smoking status (Aim 1), objective sleep characteristics and smoking behavior among blacks and whites who smoke cigarettes (Aim 2), and whether sleep restriction modifies craving and withdrawal in racially diverse smokers (Aim 3). Specifically, we will utilize self-report questionnaires, objective measures of sleep quality and timing (actigraphy) and circadian phase (dim light melatonin onset), as well as ecological momentary assessment of cigarette use, smoking urges, cravings, and withdrawal symptoms to identify circadian and sleep characteristics that are most strongly associated with smoking status, heaviness of smoking and dependence among blacks and whites. Finally, we will test whether acute sleep restriction (4 hours of time-in- bed) versus sleep extension (10 hours of time-in-bed) modifies craving and withdrawal symptoms following cessation in black and white smokers. If successful, the results of this study will result in identification of circadian dysfunction and insufficient sleep as mechanisms that underlie the association between sleep and cigarette smoking behaviors and dependence in diverse populations. Moreover, these findings are likely to inform clinicians of the importance of sleep and sleep timing on cigarette smoking behaviors and dependence that will help in the development of novel interventions to reduce morbidity and mortality caused by tobacco use.